1. Field of the Invention
The present invention is directed generally to lithography. More particularly, the present invention relates to maskless lithography.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate or part of a substrate. A lithographic apparatus can be used, for example, in the manufacture of flat panel displays, integrated circuits (ICs) and other devices involving fine structures. In a conventional apparatus, a patterning device, which can be referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of an IC, flat panel display, or other device. This pattern can be transferred onto all or part of the substrate (e.g., a glass plate, a wafer, etc.), by imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate.
The patterning device can be used to generate, for example, an IC pattern. The patterning device can additionally or alternatively be used to generate other patterns, for example a color filter pattern or a matrix of dots. Instead of a mask, the patterning device can be a patterning array that comprises an array of individually controllable elements. The pattern can be changed more quickly and for less cost in such a system compared to a mask-based system.
A flat panel display substrate is typically rectangular in shape. A wafer substrate is typically circular in shape. Lithographic apparatus designed to expose substrates of these types can provide an exposure region that covers a full width of the substrate, or covers a portion of the width (for example half of the width). The substrate can be scanned underneath the exposure region, while the mask or reticle is synchronously scanned through a beam. In this way, the pattern is transferred to the substrate. If the exposure region covers the full width of the substrate then exposure can be completed with a single scan. If the exposure region covers, for example, half of the width of the substrate, then the substrate can be moved transversely after the first scan, and a further scan is typically performed to expose the remainder of the substrate.
As is known, maskless lithography systems have been developed that replace a reticle with a patterning device including an array of individually controllable elements. The patterning device includes an active area or an array of active areas, each active area in the array having corresponding ones of the individually controllable elements, and inactive areas that include the control systems for controlling the individually controllable elements. The individually controllable elements are controlled to be positioned to form a desired pattern. These active elements are also known in the art as “pixels.” A stored control algorithm based on a desired exposure pattern is used to control the pixels. Each pixel in the patterning device can vary its optical properties (e.g., amplitude/phase transmittance) in a controllable manner so as to provide a variation of a dose delivered to the substrate surface.
As maskless lithography capabilities increase, it is important to make as efficient use as possible of a beam of radiation (e.g., illumination light), while preventing excess light from reaching a projection system of the lithography system. To ensure that the active area of the patterning device is fully illuminated, a cross-sectional footprint of the illumination beam at the active area is typically larger than the size of the active area. Light that falls outside the active area (e.g., the overfill) is referred to herein as excess light. This excess light can enter the projection system as uncontrolled light and introduce errors and/or inconsistencies into the patterned beam of the lithography system.
Therefore, what is needed is a system and method for reducing lithography errors caused by excess light, while maximizing an active area of a patterning device.